One of the oldest, most commonly utilized temperature sensing devices is the thermistor. These devices are inexpensive; however, the low cost for the temperature sensor comes with several significant drawbacks. Thermistors require the use of a separate external resistor to operate. Thermistors are extremely non-linear with temperature, dropping in resistance as temperature increases. The non-linearity provides large changes at low temperatures, but small changes at high temperatures. This phenomenon requires a very accurate Analog to Digital Converter and other components in utilization circuits and systems that utilize thermistors as temperature sensing devices.
Thermistor accuracies can vary significantly from part to part necessitating a calibration step to ensure accurate temperature measurements. A non-linear, non-calibrated thermistor is typically inexpensive. However, the associated circuitry which typically includes an analog to digital converter, a reference voltage source, non-volatile memory, and software overhead in addition to the microcontroller, add significantly to overall system cost.
It is highly desirable to provide a low power, linear, highly accurate, calibrated temperature sensor that can replace thermistors.